1. Field of the Invention
In general, the present invention relates to a storage system and a method of configuring the storage system. More particularly, the present invention relates to a storage system suitable for executing centralized management of management information of the storage system, which is capable of continuing its operation, that is, without halting the operation, when changing the storage system's configuration comprising one storage controller or a plurality of storage controllers without regard to the configuration, and relates to a method of configuring the storage system.
2. Description of the Related Art
There are a variety of storage systems, from a large-scale storage system demanded by typically a data center of an enterprise to a small-scale storage system demanded by the general open market. In either case, performance and a storage capacity required of a small or large-scale storage system greatly vary in accordance with the application.
In order to solve a problem of scalability required of a storage system, there has been proposed a conventional method whereby a switch is provided between a host computer and a storage system so as to allow an additional storage system to be connected to the host computer by connecting the switch by using a transfer path used in connecting the storage systems to the host computer.
Also in order to solve a problem of scalability required of a storage system, there has been conceived another method whereby a plurality of components are connected to each other to form a multi-component storage system which appears to a host computer as a single storage system. In accordance with this method, data transfer paths and management-information transfer paths inside the multi-component storage system are typically connected to each other to integrate the components into a single storage system.
On the other hand, a micro program of a conventional storage system is written by assuming that the storage system serving as a control object both logically and physically has a structure of a single storage system. Thus, with a plurality of small-size storage systems connected to each other to form a single storage system, if all the storage systems are not regarded logically as a single storage system, it is necessary to revise the conventional micro program's basic recognition of the storage system. In this case, a modification range involves the entire micro program and the scale of the modification becomes extremely large.
Thus, also when a plurality of components are connected to each other to form a single storage system, there is raised a demand to regard the structure of the connected components logically as the structure of the single storage system so that the micro program can be applied in a diversionary way.
If the structure of storage-system components is regarded logically as the structure of a single storage system, management information of the single storage system is information of integrity, that is, information that cannot be separated into portions of the storage-system components as is the case with the management information of the conventional storage system. For this reason, in order to store the management information, it is necessary to allocate a logically contiguous memory area as is the case with the conventional storage system.
As one of methods to allocate a memory area for storing management information, management-information memories distributed among storage-system components are used. If physically distributed management-information memories are to be managed logically as a management-information memory, however, a maintenance function becomes difficult to implement. This is because, in the conventional storage system, management information is stored in a physically single management-information memory.
Assume that a plurality of components or small-size storage systems are connected to each other to form a single storage system and, in the state in which the connected components appear as a single storage system, any arbitrary small-size storage system is removed. In this case, an area for storing a part of management area is also removed as well. Since the management information is information of integrity which cannot be separated into portions, the management information becomes unusable even if only a part thereof is lost. Thus, if any arbitrary small-size storage system is removed, it is necessary to halt the operation of the storage system.
By the way, members other than management-information memories each used for storing management information are also distributed among small-size storage systems. In implementation of a maintenance function for such members, the conventional maintenance method can be adopted in a diversionary way relatively with ease. This is because, the conventional storage system also has functions to partially block, maintain and recover configuration elements other than the management-information memories.
As described above, the conventional technology provides a method whereby a plurality of components or small-sized storage systems are connected to each other to form a single storage system. However, this method has the following problems.
In the method whereby a plurality of components or small-sized storage systems are connected to each other to form a single storage system, a technique to manage all the small-sized storage systems is not taken into consideration.
Thus, an attempt made to apply the micro program of the conventional storage system raises a problem that the scale to modify the micro program becomes extremely large and the diversionary application of the micro program becomes difficult.
In addition, the method whereby a plurality of components or small-sized storage systems are connected to each other to form a single storage system does not consider a technique to store the storage system's management information of integrity that cannot be separated into portions of the small-size storage systems in management of the small-sized storage systems as a logically single storage system.
Thus, management information is stored in management-information memories employed in the physically distributed small-size storage systems, making the maintenance function difficult to implement. In addition, there is also raised a problem that, since the management information is also physically distributed, performance to make accesses to management information deteriorates as well.
Furthermore, in the conventional technology, a flexible technique of coping with changes in storage-system configuration is not taken into consideration either.
For example, when the storage-system configuration is changed from a configuration comprising a component of a storage system to a configuration comprising a plurality of components composing the storage system, making it necessary to transfer management information from one location to another, the operation of the storage system must be halted, raising a problem that a host is not capable of making an access to a disc storage in the mean time. This problem becomes serious in particular in a version-up process of a large-scale storage system which must be operated all the time.